Motor controller

Abstract

A motor controller includes a motor, an encoder, and a control circuit. The motor drives a target object to be controlled. The encoder outputs a pulse signal synchronously with rotation of the motor. The control circuit rotates the motor based on a count value of the pulse signal. The control circuit switches to a sleep mode when making sure that a rotation position of the motor is stable after finishing rotating the motor or when a predetermined time necessary for the rotation position of the motor to be stable elapses after finishing rotating the motor. When a change in the pulse signal during a period of time where the control circuit is in the sleep mode is not smaller than a predetermined amount, the control circuit performs a learning process to learn a reference position of the motor when returning to a wakeup mode from the sleep mode.

What is claimed is: 
     
       1. A motor controller comprising:
 a motor that drives a target object to be controlled; 
 an encoder that outputs a pulse signal synchronously with rotation of the motor, and 
 a control circuit that rotates the motor based on a count value of the pulse signal, wherein 
 the control circuit switches to a sleep mode when making sure that a rotation position of the motor is stable after finishing rotating the motor or when a predetermined time necessary for the rotation position of the motor to be stable elapses after finishing rotating the motor, and 
 when a change in the pulse signal during a period of time where the control circuit is in the sleep mode is not smaller than a predetermined amount, the control circuit performs a reference position learning process to learn a reference position of the motor by rotating the motor when returning to a wakeup mode from the sleep mode. 
 
     
     
       2. The motor controller according to  claim 1 , further comprising:
 an encoder counter that counts the pulse signal outputted from the encoder during the period of time where the control circuit is in the sleep mode, wherein 
 when a change in a count value of the encoder counter during the period of time where the control circuit is in the sleep mode is smaller than a predetermined value, the control circuit does not perform the reference position learning process when returning to the wakeup mode. 
 
     
     
       3. The motor controller according to  claim 2 , wherein
 when the change in the count value of the encoder counter during the period of time where the control circuit is in the sleep mode is not smaller than the predetermined value, the control circuit performs the reference position learning process when returning to the wakeup mode. 
 
     
     
       4. The motor controller according to  claim 1 , wherein
 the motor control circuit is electrically connected to a battery through a connector, and 
 when the connector is disconnected from and connected back to the motor control circuit or the battery during the period of time where the control circuit is in the sleep mode, the control circuit performs the reference position learning process when returning to the wakeup mode. 
 
     
     
       5. The motor controller according to  claim 1 , wherein
 the motor control circuit is electrically connected to at least one of the motor and the encoder through a connector, and 
 when the connector is disconnected from and connected back to the motor control circuit or the at least one of the motor and the encoder during the period of time where the control circuit is in the sleep mode, the control circuit performs the reference position learning process when returning to the wakeup mode.